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terça-feira, 16 de setembro de 2008

Reactor nuclear para a base lunar

NASA is tip-toeing once again into what was once called the N-word -- nuclear -- with a technology development program aimed at powering its planned base on the moon.

The goal of the Fission Surface Power Project, which is based at NASA's Glenn Research Center in Cleveland, Ohio, is to produce a non-nuclear prototype unit within five years.

NASA's last foray into nuclear technologies was a project that began in 2003 known as Prometheus, which focused on both nuclear propulsion and nuclear-powered generators that ultimately could be used to support a manned mission to Mars and for deep-space probes, such as a mission to Jupiter's ocean-bearing moon Europa.

Prometheus was preceded in the 1950s and 60s by the NERVA, Project Orion and other initiatives.

Prometheus ended, but a small-scale effort to develop a compact, highly autonomous fission reactor as part of the agency's new exploration initiative, Project Constellation, survived. The program aims to return U.S. astronauts to the moon by 2020 and establish a base before moving on to manned missions to Mars and other bodies in the solar system.

Supported at a cost of about $10 million a year, the Fission Surface Power Project this week awarded two contracts for power conversion units, used to turn the heat of nuclear reactions into electricity.

NASA envisions needing a system capable of providing about 40 kilowatts of electricity -- about what's used to power eight average homes in the United States.

It would be launched cold and without radioactive elements until operations were to begin on the lunar surface.

NASA is thinking about burying the system so the lunar soil can serve as shielding.

The converter design by Sunpower Inc., of Athens, Ohio, uses two opposed piston engines coupled to alternators to produce a total of 12 kilowatts of power. Barber Nichols Inc. of Arvada, Colo., is developing a closed Brayton cycle engine that uses a high-speed turbine and compressor coupled to a rotary alternator. It also generates 12 kilowatts.

The ground system would not use any nuclear materials, said project manager Lee Mason.

"Our goal is to build a technology demonstration unit with all the major components of a fission surface power system and conduct non-nuclear, integrated system testing in a ground-based space simulation facility," he said.

A space-based reactor would have to be much more compact than fission reactors currently operating on Earth and would generate far less power. The agency also is looking at solar-powered technologies, fuel cells and other systems.

Among engineers' challenges are the harsh, radioactive environments and the extreme temperature ranges of space.

The moon's 29.5-day rotational period produces long, cold nights lasting 354 hours, which presents a formidable challenge for solar-powered systems. On Mars, the night-time is just 12 hours, but its distance from sun means only 20 percent of the energy that reaches the moon makes it to Mars.

"As you get further and further out, the missions get longer and longer, and you're going to have to have higher and higher power levels," said John Warren, who oversees the program at NASA headquarters in Washington D.C. "You're probably going to have to have nuclear, and I think that will be recognized not only here in the U.S., but around the worl